1. Field of the Invention
The present invention relates to a method and related apparatus of default timer configurations of wireless communications system, and more particularly to a method and related apparatus for decreasing delay of a reset procedure.
2. Description of the Prior Art
The third generation (3G) mobile communications system has adopted a Wideband Code Division Multiple Access (WCDMA) wireless air interface access method for a cellular network. WCDMA can provide high frequency spectrum utilization, universal coverage, and high quality, high speed multimedia data transmission. The WCDMA method also meets all kinds of QoS requirements simultaneously, providing diverse flexible two-way transmission services and better communication quality to reduce transmission interruption rates. Taking Universal Mobile Telecommunications System (UMTS) as an example, the 3G mobile communications system is composed of User Equipment (UE), UMTS Terrestrial Radio Access Network (UTRAN), and Core Network (CN), using communications protocols of Access Stratum (AS) and Non-Access Stratum (NAS). Targeting the AS, the 3G mobile communications system defines various protocol stacks, such as Radio Resource Control (RRC), Radio Link Control (RLC), Media Access Control (MAC), Packet Data Convergence Protocol (PDCP), and Broadcast/Multicast Control (BMC).
To implement functions of the aforementioned protocol stacks, the 3rd Generation Partnership Project (3GPP) has established related communication protocol specifications as its website, www.3gpp.org, presents. The communication protocol specifications provide default configurations for variables and parameters, so as to enhance system efficiency, and to reduce the signaling messages during radio connection setup for a UE. However, some default configurations may affect system operations, causing waste of radio resources. For example, in a communications protocol specification established by the 3GPP(3GPPTS 25.331 V6.9.0 (2006-03), “Radio Resource Control (RRC) protocol specification”), the default value of a timer Timer_RST in the uplink configuration is set to be 300 ms (millisecond), a timer Timer_Poll in the uplink configuration is not configured by default, and the default value of a timer Timer_Status_Prohibit in the downlink configuration is set to be 100 ms. However, in another communications protocol specification established by the 3GPP (3GPP TS 34.108 V6.2.0 (2006-03), “Common test environments for User Equipment (UE); Conformance testing”), the default values of the timers Timer_RST and Timer_Poll in the uplink configuration are set to be 500 ms and 200 ms respectively, and the default value of the timer Timer_Status_Prohibit in the downlink configuration is set to be 200 ms.
The timers Timer_RST, Timer_Status13 Prohibit, and Timer_Poll are all used for RLC entities (of UE or/and UTRAN) to hold retransmission of a control signaling (RESET PDU, STATUS report, or polling) until the expected response from the peer RLC entity is received. Note that, descriptions of the three timers can be found in the RLC communications protocol specification established by the 3GPP, and will not be narrated in detail. Thus, all the three timers should be equal to or longer than the round trip time (RTT), which is the time duration between the instant when the signaling is sent out and the instant when the response message is received. To cover variance of processing powers among different UE implementations, the timers are generally configured to be larger than RTT.
In the specifications 3GPPTS 25.331 V6.9.0 and 3GPPTS 34.108 V6.2.0, the default values of the timers are different, and the default value of the same timer is inconsistent, causing system efficiency degradation.
For example, in 3GPP TS 25.331 V6.9.0, the timer Timer_Status_Prohibit is set to be 100 ms, meaning that RTT is shorter than 100 ms, but the timer Timer_RST is set to be 300 ms. Thus, a RESET PDU will be held for 300 ms before it can be retransmitted if a RESET ACK PDU corresponding to the RESET PDU is not received by the sender. However, since RTT is shorter than 100 ms, if the RESET ACK PDU is not received within 100 ms, the RESET ACK PDU will never arrive later. Thus, retransmission of the RESET PDU is delayed 200 ms (300−100=200) longer than needed. The reset procedure is delayed.
Similarly, in 3GPP TS 34.108 V6.2.0, the timers Timer_Status_Prohibit, and Timer_Poll are all set to be 200 ms, meaning that RTT is less than 200 ms. However, the timer Timer_RST is set to be 500 ms. Thus, retransmission of the RESET PDU is delayed 300 ms (500−200=300) longer than needed. The reset procedure is also delayed.